DETROIT (Reuters) -- U.S. safety regulators have upgraded the investigation of an estimated 335,195 Honda Accord sedans a step closer to a recall after receiving almost 300 complaints that airbags can deploy when the car door is shut with too much force.

The National Highway Traffic Safety Administration said in documents filed online on Friday that it was upgrading the investigation to an "engineering analysis" from a "preliminary evaluation" of the 2008 four-door models made by Honda Motor Co.

An engineering analysis is a step that can lead to a recall if regulators determine that the manufacturer needs to address a safety problem.

NHTSA said it had identified 293 incidents of alleged inadvertent deployment of driver or passenger side airbags. Fourteen people were injured because of the problem, according to the agency's documents.

In some cases, the side seat-mounted torso airbag can deploy as well, NHTSA said.

NHTSA said it was investigating the risk of airbag deployment injuries to occupants in vulnerable positions. Regulators opened the initial preliminary evaluation in late January.

Honda said it was aware of the upgraded investigation "based on a small number of complaints," adding that "Honda will continue to cooperate with the NHTSA through the investigation process, and we will continue our own internal review of the available information."

In June 2008, near the end of 2008 model-year Accord production, Honda changed the crash parameter for door-closing force in the electronic control unit's software code to reduce the incidents of inadvertent side airbag deployments, NHTSA said. Regulators found the number of inadvertent airbag deployments had fallen significantly after that.

Honda said the two-door Accord used a different software crash parameter than the four-door model, according to NHTSA.

In one incident last fall, an owner said he had stopped at a gas station so his fiancée could purchase a drink. When she closed the door, the passenger-side curtain airbag deployed, striking their 9-year-old son, according to a complaint filed with NHTSA.

The boy had a concussion and blood behind the ear, according to the complaint.